I would highly recommend K's place.
The place itself is beautiful. Full of nooks and crannies, it's one of the most homely places I've stayed in.
The location, though relatively far from the most centrally tourist areas of Bangkok, also in my view benefits from being far relatively far from the most centrally tourist areas of Bangkok! It's a quieter local neighbourhood that gives a more "real" sense of Bangkok than more central locations. Having said though if you want to go to the more tourist areas, K's place is still very close to the MRT which will get you elsewhere pretty quickly.
As for K himself and his mother Apple, they are amazing hosts. Incredibly warm, they even check in with you via Airbnb from time to time when you're out and about just to make sure everything is going well for you.
Oh and they make some very good food in their restaurant also!
This is a clear cut 5 star review